Electroacoustic bandpass filter having smoothed insertion loss

Abstract

A bandpass filter operates with electroacoustically active components. The bandpass filter includes a first transducer segment having a spike in the insertion loss at a first frequency f 1 and a second transducer segment having a spike in the insertion loss at a second frequency f 2 ≠f 1 . The frequencies f 1 and f 2 are chosen such that the insertion loss is smoothed.

The invention claimed is: 
     
       1. An electroacoustic bandpass filter comprising:
 a piezoelectric layer having an acoustic track; and 
 a metallization layer arranged on the piezoelectric layer and in the acoustic track; 
 wherein the acoustic track comprises a first section and a second section; 
 wherein in the first section, a first transducer segment is formed in the metallization layer, the first transducer segment forming a resonance at a first frequency f 1  and generating a spike in insertion loss; 
 wherein in the second section, a second transducer segment is formed in the metallization layer, the second transducer segment forming a resonance at a second frequency f 2  and generating a spike in insertion loss, where f 2 ≠f l ; and 
 wherein the frequencies f 1  and f 2  are chosen such that the manifestation of the spikes in insertion loss of the filter is reduced compared with the manifestation of the spikes of the individual transducer segments. 
 
     
     
       2. The electroacoustic bandpass filter according to  claim 1 , wherein the first transducer segment is part of a first transducer and the second transducer segment is part of a second transducer, the first and second transducers being different frequency-offset transducers. 
     
     
       3. The electroacoustic bandpass filter according to  claim 2 , wherein the first and second transducers are cascaded and interconnected in series or in parallel. 
     
     
       4. The electroacoustic bandpass filter according to  claim 3 , wherein the first and second transducers are part of a resonator cascade with a common busbar. 
     
     
       5. The electroacoustic bandpass filter according to  claim 1 , wherein the first transducer segment and the second transducer segment are two segments of the same transducer. 
     
     
       6. The electroacoustic bandpass filter according to  claim 5 , wherein the first transducer segment and the second transducer segment are two segments of a FAN-type transducer. 
     
     
       7. The electroacoustic bandpass filter according to  claim 1 , wherein the filter is a SAW filter or a GBAW filter. 
     
     
       8. The electroacoustic bandpass filter according to  claim 1 , wherein:
 the first transducer segment and the second transducer segment are arranged in a first transducer; and 
 the filter comprises a second transducer and is a DMS filter or a multi-port resonator filter. 
 
     
     
       9. The electroacoustic bandpass filter according to  claim 1 , further comprising a reflector, which is configured as a FAN-type reflector. 
     
     
       10. The electroacoustic bandpass filter according to  claim 9 , wherein the FAN-type reflector has a pitch scaling of between 500 ppm and 2000 ppm. 
     
     
       11. The electroacoustic bandpass filter according to  claim 9 , wherein the piezoelectric layer has an underside which at least partly reflects bulk acoustic waves and the FAN-type reflector is provided for scattering bulk acoustic waves in order to reduce the ripple of the insertion loss. 
     
     
       12. The electroacoustic bandpass filter according to  claim 1 , wherein the filter is a DMS filter and the transducer is a partial FAN-type transducer or a complete FAN-type transducer. 
     
     
       13. The electroacoustic bandpass filter according to  claim 12 , further comprising a third transducer, wherein the first transducer, the second transducer and the third transducer are FAN-type transducers, and wherein two of the transducers are output transducers and one of the transducers is an input transducer arranged between the output transducers. 
     
     
       14. The electroacoustic bandpass filter according to  claim 13 , wherein the piezoelectric layer has an underside which at least partly reflects bulk acoustic waves and the FAN-type transducers are provided for scattering bulk acoustic waves in order to reduce the ripple of the insertion loss. 
     
     
       15. The electroacoustic bandpass filter according to  claim 1 , further comprising a parallel branch transducer having a pitch P 2 , wherein one of the first and second transducer segments is arranged in a series branch transducer having a pitch P 1  and P 2 >P 1 . 
     
     
       16. The electroacoustic bandpass filter according to  claim 1 , wherein the frequencies f 1  and f 2  are chosen such that undesirable Fabry Perot resonances are reduced.